The present invention is concerned with a method and apparatus for making parallax determinations and, more particularly, it is concerned with a method for automatically making parallax determinations in stereoscopic, optical systems, preferably binary optical systems, having at least one movable grating structure in the path of imaging light. Such systems can be, for example, base range finder systems. The parallax determination is made on the basis of differentiable luminous fluxes which are converted into electrical signals. The invention is further concerned with apparatus for carrying out such determinations.
In stereoscopic optical systems, it is generally desirable that the parallax between two partial images be determined automatically. This is particularly so in the case of base range finders, or in connection with the analysis of aerial stereo photographs. Various systems for optical-electrical scanning and for the subsequent use or processing of the resulting electrical signals have already been suggested for these purposes.
One such prior art system is shown in FIG. 1 of the drawing, where the fundamental wave of the resulting signals is being utilized. Two objective lenses 10 and 11, which define two light channels, project an image of an object (not shown) onto a grating structure 16, via deflecting mirrors 12, 13, 14 and 15. The grating structure is movable perpendicularly with respect to the optical axes 18 and 19 by means of a drive 17' which is controlled by a generator 17. In line with each optical axis a photoelectric receiver 20 or 21, respectively, is arranged which converts the light portions which have passed through the grating structure 16 into electrical signals. Each of the two receivers 20 and 21 is connected to a phase discriminator or comparator 22 or 23, respectively, which is controlled by means of a reference signal received from the generator 17. The output of the discriminator 22 of the first light channel is connected to the drive 17' of the grating structure 16 via a control member 24. The output of the discriminator 23, in turn, controls an adjustment mechanism 25 via a control member 26. The mechanism 25 provides mechanical means for pivoting the mirror 15 along the direction of the arrow as indicated.
The operation of the system of FIG. 1 is such that the first light channel determines the position phase difference and, with the aid of the control member 24, shifts the median position of the grating structure 16 until it reaches the point where the output signal of the phase discriminator 22 reaches zero. At this point, the phase discriminator 23 indicates the parallax. The control member 26 and the drive 25 for the mirror 15 serve to adjust the resultant parallax to zero.
One shortcoming of this prior art system is that it requires two feedback loops which are coupled by the grating structure.
U.S. Pat. No. 3,710,124 describes a method which uses the fundamental wave and the second harmonic of the grating frequency. A shortcoming of the method disclosed in the patent, as can be demonstrated, resides in that the accuracy of the measurement obtained is dependent upon the accuracy with which the amplification has been adjusted and the latter, in turn, is dependent on the amplitude of the fundamental wave and of the second harmonic, respectively.